As is well known in the art, composite plating uses composite plating solutions which are nickel and similar metal plating solutions having insoluble particles such as zirconia and alumina dispersed therein. With articles dipped in the solutions, deposition is electrically or chemically induced to form a composite deposit on the article wherein insoluble particles are co-deposited and dispersed in a metal matrix. Typically zirconia or alumina is co-deposited in nickel. The composite deposits serve for various functions including wear resistance, heat resistance and heat insulation, and any desired combination of such functions is accomplished by a choice of particular types of matrix metal and insoluble particles. In order to exert such functions more effectively, it is necessary to control the amount of insoluble particles co-deposited so as to provide an optimum amount of insoluble particles dispersed in the metal matrix.
While it is desired to control the amount of insoluble particles co-deposited in the metal matrix in accordance with a particular application, it is also recently desired to provide a composite deposit with differential functions in that the amount of insoluble particles co-deposited is different between the inside and outside of the deposit. For producing composite deposits having graded functions, it is essential to freely control the amount of insoluble particles co-deposited.
In the prior art, the amount of insoluble particle co-deposited is controlled by various means, such as by increasing or decreasing the amount of insoluble particles dispersed in plating solution or adjusting plating conditions, for example, adjusting the agitation speed of plating solution, adjusting the plating temperature, or in the case of electrodeposition, increasing or decreasing the current density. The adjustment of the amount of insoluble particles dispersed in plating solution has a certain limit in that although an increased amount of particles dispersed generally leads to an increased amount of particles co-deposited, the amount of particles dispersed cannot be increased beyond a practically acceptable level. The adjustment of plating conditions is insufficient to control the amount of particles co-deposited over a wide range.
Therefore, there is a need for a composite plating method capable of effective control of the amount of insoluble particles co-deposited.